Recorded observations of how the Earth's
climate has changed over the last 50 years can substantially
help scientists predict future climate change, according to an
international team of scientists. Using a synthesis of computer
models and observed data along with a common assumption about
future emissions of greenhouse gases and other pollutants, the
team expects that global mean temperature in the decade 2036-2046
will be 1.8 to 4.5 degrees Fahrenheit warmer than pre-industrial
conditions. This temperature range can be expected to narrow
as further observations become available.

In a study to be published in the October
5 issue of Nature,
scientists used a novel statistical technique to refine estimates
of climate change produced by leading computer climate models
around the world. The team, which was led by Myles Allen of Rutherford Appleton Laboratory
and included Thomas Delworth of NOAA's
Geophysical Fluid Dynamics
Laboratory, assembled climate change projections from climate
modeling centers in the United States, England, and Germany.
Knowledge of how well those computer models simulated climate
change that was observed over the last 50 years was used to refine
forecasts of future climate change.

"For the first time, we are using
observations of climate change as it's happening to pin down
what is likely to happen next," according to Allen.

"The technique attempts to statistically
compensate for inherent limitations in climate models,"
according to Delworth. "This technique does not, however,
address uncertainties related to future emissions of greenhouse
gases and other pollutants."

Projections of future climate change are
hindered both by uncertainties in the computer models used for
such projections, as well as uncertainties in future emissions
of greenhouse gases. "This study only addressed the former
of those two issues."

While the goal of the study was to assess
the uncertainty in the projection of future climate change, the
authors note that the study assumes that the general character
of climate change over the next 50 years will be closely related
to changes observed over the last 50 years. In addition, future
emissions of greenhouse gases and other pollutants which differ
from the assumptions used in this study will alter the projections
of climate change. "There is clearly the potential for substantial
surprises in future climate change," according to Delworth.